Lead-and manganese-activated cadmium-sodium fluorophosphate phosphor



United States Patent() LEAD- AND MANGANESE-ACTIVATEDy CAD- MIUM-SODIUMFLUOROPHOSPHATE PHOS- PHOR Robert W. Wollentin, Bloomfield, N. J.,assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., acorporation of Pennsylvania Application January 24, 1955, Serial No.483,617

4 Claims. (Cl. 252-301.@

This invention relates to luminescent materials and. more particularly,to luminescent materials having a predominantly red color whenirradiated by 2537 A. U.

It is the general object of this invention to provide a leadandmanganese-activated cadmium-sodium fluorophosphate luminescent materialwhich will have a predominantly red color when irradiated by 2537 A. U.

It is another object to provide optimum and permissible ranges for theraw-mix components of the phosphor and to provide a method of makingsame.

The aforesaid objects of the invention, and other objects which willbecome apparent as the description proceeds, are achieved by providing aleadand manganeseactivated cadmium-sodium tluorophosphate luminescentmaterial wherein the molar ratio of cadmium orthophosphate to sodiumfluoride is from 3:2.5 to 3:5.5 and the lead and manganese activatorsare maintained within allowable ranges.

For a better understanding of the invention, reference should be had tothe accompanying drawing wherein:

Fig. l is a spectral distribution curve of relative energy vs. wavelength in Angstrom units for the preferred ernbodiment of the phosphorof this invention;

Fig. 2 is a graph representing relative brightness vs. moles of sodiumfluoride per 3 moles of cadmium orthophosphate for cadmium-sodiumtluorophosphate phosphor activated by manganese and lead.

Fig. 3 is a graph representing relative brightness vs percent manganeseby Weight of cadmium orthophosphate for cadmium-sodium fluorophosphatein which the amounts of lead activator are also varied.

With specific reference to the spectral distribution curve illustratedin Fig. l, the cadmium-sodium uorophosphate luminescent material has inits preferred form Ia spectral distribution which is peaked at about6200 A. U. In this spectral distribution curve the most intenseincrement of observed value of radiation is arbitrarily set at arelative energy or relative value of 100 and the remaining measuredincrements of the spectral distribution are correlated to this value of100 and plotted accordingly.

The preferred embodiment for the cadmium-sodium liuorophosphateluminescent material has the general formulation: 3Cd3(PO4)24NaF:O.4%Mn:4%Pb, with an excess of from l to molar percent of P205. It l ICCshould be noted that all activator percentages and molar excess of P205are with respect to the cadmium orthophosphate.` The effect of varyingthe moles of sodium fluoride per 3 moles of cadmium orthophosphate areillustrated in Fig. 2 wherein a peak in relative brightness is observedwhen the molar ratio of cadmium orthophosphate to sodium uoride is 3 to4. The limitations in permissible molar ratios of cadmium orthophosphateto sodium fluoride are indicated in dotted lines as being from 3 to 2.5to 3 to 5.5. These permissible limitations are selected on a purelyarbitrary basis from brightness data which is represented in the curvein Fig. 2, the selection being governed by what constitutesacommercially acceptable and competitive phosphor. It should be notedthat the relative brightness measurements as indicated in Figs. 2 and 3were made with a Weston type 3 Photronic Cell, equipped with an eyesensitivity filter so that the photocell sensitivity was substantiallythe same as the sensitivity of the eye. As illustrated in Fig. 2, wherethe cadmium orthophosphate to sodium uoride ratio is 3 to 2.5, thephosphor will have a relative brightness of about 52 rising to a maximumbrightness of 621/2 at a ratio of 3 to 4 and thereafter decreasing to arelative brightness of about 57 at a ratio of 3 to 5.5.

In Fig. 3 is illustrated how the phosphor brightness is varied byvarying the activator percentages where the cadmium orthophosphate andsodium fluoride are present in optimum molarproportions. Based on therelative brightness obtained, and arbitrarily basing the permissibleactivator proportions on these observed brightnesses, as dictated bywhat constitutes a commercially acceptable phosphor, it has been foundthat the percent by weight of manganese activator should be at least0.1% by weight and not more than 1% by weight of the cadmiumorthophosphate with the optimum output occurring at about 0.4% ofmanganese by weight. The permissible range of lead activator is from0.5% to 7% by cadmium orthophosphate weight and the optimum outputoccurs at 4% with the manganese activator present in optimumproportions. If the percent by weight of the manganese activator iswithout the heretofore given range, the phosphor brightness will not besatisfactory for the usual application in gas-discharge lamps. If thepercent by weight of lead activator is below the heretofore givenallowable range, the phosphor emission peak will tend to shift to theleft and if the percent by weight of the lead activator is above theaforementioned permissible range, the phosphor when fired will tend tosinter excessively. In addition, the phosphor color changes from whiteto gray with excessive lead activator concentrations which gray colordecreases the phosphor efficiency. It should be noted that wheneverpercentages of activator proportions are given, the percentage by weightof cadmium orthophosphate is intended. For example, where 4% by weightof lead activator is referred to, the total weight of metallic leadpresent is 4% yof the Weight of the cadmium orthophosphate in thephosphor.

Varying the leadand manganese-activator concentrations will shift thcemission peak somewhat, the greater the concentrations of activator, thefurther the emission peak is `shifted to the right. There is shown inthe following table, indicated as Table I, the effect of varying thelead and manganese concentrations, and as will be observed the emissionpeak occurs at 6200 A. U. for the optimum proportions of activator,which emission peak is indicated as )t max, It should be noted thatincreasing the lead :and manganese activator concentrations will shiftthe emission peak to the right of 6200, i. e. toward the longer wavelengths, which shift is desirable to increase further the percentage ofred radiation. However, the relative brightness is considerablydecreased from the relative brightness of a phosphor having the optimumactivator concentrations.

TABLE I Eect of activator concentration on emission peak of 3Cd3 (P04) z4N aF :M mPb Percent Percent n Pb :err-PPQQPPQPPPPPQOOOOONNOOOBDNOONOObN potecwoessasueteteasesopss: GO OOOOOOOOOOCHUIM 1Preferred embodiment.

Norn.-Activators are expressed in percent by weight of cadmiumorthophosphate.

In preparing the preferred embodiment of the leadand manganese-activatedcadmium-sodium tluorophosphate luminescent material of this invention,the following rawmix components may be mixed in proportions as givenbelow.

The above raw materials are thoroughly mixed by ballmilling or otherconventional mixing techniques and, as an example, 4a mixing time of 30minutes is generally satisfactory. The ballmilling may be followed by aten minute hammermilling and another minutes of ballmilling if desired.These mixing times are more 'a matter of choice and are not critical,and are only given as an example. The mixed, blended raw materials arethen placed in covered -silica trays 'and fired in' an air atmosphere:at between 450 C. to 600 C. for one or more hours, and as a Ispecificexample, the phosphor may be tired at 580 C. for one hour. A secondmilling and ring cycle, similar `to that as heretofore given, may bedesired in order to insure a complete reaction of the raw r ingmaterials.

materials, although the second milling and tiring cycle is notnecessary.

Many different raw-mix materials may be substituted for the materialsgiven in the foregoing example and the 'resulting luminescent materialwill be the same. Broadly, the -raw-mix materials may be broken downinto four main categories. Cadmiumand phosphorusand oxygen-containingmaterial which when fired will form Cd3(PO4)2 with an excess of from 1to 50 molar percent of P205 over the total moles of Cds(PO4)2 whichwould be formed if all of the cadmium were present as theorthophosphate. The optimum excess of P205 present in the raw mix is 25molar percent. In other words, if there are 9 moles of CdO and 7.5 molesof (NH4) 2-HPO4 in the raw mix and these components are suitably mixedand then tired, the resulting compound may be expressed as 3 moles ofCda (PO4)2 with an excess vof 0.75 mole of P205. Actually this P205 mustbe chemically combined with the cadmium as metaphosphate, orthophosphateand various intermediate complexes. However, a chemical `analysis willshow only so much CdO and so much P205, without showing how these oxidesare combined. Thus a representation of so much Cd3(PO4)2 with so muchexcess of P205 is accurate from an analytical standpoint and enables thecompound to be identified accurately. Also for the purposes ofidentifying the rawmix components, it is immaterial just how thesecombine on firing, as long as the desired excess of phosphate ispresent. It is, of course, understood that the Cd3(PO4)2 formingmaterial should be free from nou-volatile constituents other than theessential elements constituting the phosphor, namely cadmium, fluorine,phosphorus, oxygen, manganese, lead and sodium. Second, a sodiumlanduorine-containing material which will form sodium fluoride on firing,and which material is free from non-volatile constituents other than theessential elements of the phosphor. Third, a lead-containing materialwhich will form lead oxide or lead phosphate on tiring and whichmaterial is free from non-volatile constituents other than the essentialelements of the phosphor. Fourth, a manganese-containing material whichwill form either manganese -oxide or manganese phosphate on tiring andwhich manganese-containing material is free from nonvolatileeonstituents other than the essential elements of the phosphor. When theaforementioned products of formation of the raw materials, for example,MnO or 'Mns (P002 are referred to, it is not meant that such compoundsactually exist as such in the red and prepared phosphors. What is meantis that raw-mix materials which can form these products when firedindividually will be satisfactory as raw-mix components for theluminescent material of this invention. Following are four tables inwhich are listed raw-mix components which may be used to form thephosphor. These `tables lare broken down as follows: Table II listscadmium orthophosphate and excess P205 forming materials; Table IIIlists sodium fluoride forming materials; Table IV lists lead oxide yandlead phosphate forming materials; Table V lists manganese oxide andmanganese phosphate form- Any of the individual cadmium orthophosphateforming compounds as given in Table II may be mixed with any of theindividual sodium uoride forming compounds as given in Table III, plusany of the lead oxide or lead phosphate forming compound as given inTable IV plus any of the manganese oxide or manganese phosphate formingcompounds as given in Table V in order to form a suitable raw-mixcomposition for the phosphor, provided the proportions of one componentwith respect to the other components are maintained in the sameproportions as are given under the columns headed Molar Ratios.

TABLE 1I Cda(PO4)z forming materials Molar Ratios Compound (numericaldesignation and optimum l Maximum specific examples in moles) Minimummoles moles phosphate conphosphate taining material containing material(l) 3CC13(PO4)2+1.5(NH4)1HP O4 06(NH4)2HP Oi 3(NH4)2HP 04 (2) 9Cd0+7 NH4HP 4 6. 06 9 (3) 9CdCO3+7.5(NHi)2HPO4 6 06 9 (4) 9CdN0a 4H20+7.5(NH4)2H6 06 9 (5) 9000204 3H2O+7.5(NH4)2HPO4 6 06 9 (6) CzH302)2-3H20-I7 5(NH42 6 06 Y 9 (7) 9Cd(OH)zI-7 5(NH4)2HP04 6 06 V9 (8) 9C 3.75 2 3 03 4.5(9) 9CdO-l-7-5H3PO4... (i 06 9 (10) 9CdO+7.5NH4H2PO4- 6 05 9 Norm-Any ofthe Cd compounds above can be used with P105 or HaPOi or NH4Hz P.O4.Also, a part of the excess P205 may be supplied from the leadandmanganesc-contammg materials noted in Tables IV and V.

TABLE III TABLE V 30 NaF forming materials MnO,Mm(POi)2 formingmaterials Molar Ratios I 3.5 Molar Ratios Compound (numericaldesignation and OOmPOlmd (Illlmrieal dffsgllatlon and moleS optimumspecific example in moles) of optimum specnic example) Minimum MaximumMinimum Maximum (11) 4NaF 2.5 5. 5 (34) 0. 0.029 0.29 (12) 2(Na2+2NH4F)l. 25 2. 75 (35) 0 0. 010 O. 10 fia) zunimmt-210mm- 1.25 2. 75 40 (36) 00. 029 0.29 14) 4(NaNO5+NH.F)- 2.5 5.5 (37) 0- 0.029 0.29 15)2(Na2C042NH1 1.25 2. 75 (38) 0- 0. 029 0. 29 (16) iNaCnHaOz-l-Nll) 2. 55 5 (39) 0. 0.029 0. 29 (1g) 4 NF'H'FNH) 2 5 (iii g`115Mn(No 3 i (l NaCOH'N m) 2 5 (42) 0.115Mno10. o. 02g 0, 29 45 (43)0.115Mn(C2HaOz)2-4H:0--- 0. 029 0. 29 (44) 0.115Mn(OH)z 0. 029 0.29 (45)0.115MnC4H405 0.029 0.29

TABLE -IV PbO,Pb3(PO4)2 forming materials Molar Ratios Compound(numerical designation and optimum speoic example in moles) MinimumMaximum (19) 0.306Pb0 0.038 0. 54 (20) 0.30610005...`- 0.038 0.54 (21) 06Pb Oz): 0.038 0. 54 (22) 0.4022PbCOa-Pb(OH)2 0. 013 0.18 (23)0.306Pb(C2H302)2-8H20 0.038 0.54 (24) 0.306Pb Hal' es (i. e., F, Cl, Br,I). 0.038 0. 54 (25) 0.306Pb(0H)2 0.038 0.54 (26) 0.106Pb304 0.013 0.l8(27) 0 158103203.` O. 019 0.27 (28) 0.306Pb 0.038 0. 5i (29)0.106Pb3(P04)2 0.013 0.18 (30) All of Pb compounds of 19, 20, 21, 22,23, 24, 25+(NH02HP in molar amounts as indicated.

(3l) All of Pb compounds of 19, 20, 21, 22, 2S, 24, 25|H3PO1 in molaramounts as indicated.

(32) All of Pb compounds of 19, 20, 2l, 22, 23, 24, 25+NH4H2P04 in molaramounts as indicated.

(33) All oi Pb compounds of 19, 20, 21, 22, 23, 24, 25d-P205 in molaramounts as indicated.

Norm-0.306 mole Pb in Example 20 is equivalent to 4%"Pb by weight ofcadmium orthophosphate in preferred phosphor as given in Example l..Also, in Examples 30-33 (inclusive) the additional phosphate-containingreactants should be used in amounts sufiicient to stoichiometricnllycombine with the lead-containing reactants.

Norm-0.115 molleV Mn in Example 34 is equivalent to 0.4% Mn by weight ofcadmium orthophosphate in preferred phosphor as given in Example l.

It will be recognized that the possible combinations of raw-mixcomponents included under the foregoing Tables II-V are numerous andeach of these plurality of raw-mix combinations are 4satisfactory forforming the luminescent material of this invention. Also, the componentslisted under the foregoing tables are by no means complete, but are onlyindicative of what constitutes satisfactory raw-mix components.

It should be under-stood that the molar ratios as given in Tables II-Vwill a-ll produce an equivalent amount of the desired material. Forexample, 0.158 mole of P13203 (see numerical designation 27) willcontain the same amount of lead as 0.306 mole of PbCOs (see numericaldesignation 20). v

It will be recognized that the objects of the invention have Vbeenachieved by providing a leadand mangaf ucsc-'activated cadmium-sodiumiluorophosphate luminescent material having :a radiation which is peakedat about 6200 when irradiated by 2537 A. U. In addition, there areprovided optimum and permissible ranges for the raw-mix components ofrthe material in addition to a method of making same.

As a possible `alternative embodiment, potassium uon'de may besubstituted for the sodium iiuoride to 7 produce luminescent materialhaving a predominantly red output.

While in accordance with the patent statutes one best known embodimentof Ithe invention has been illustrated and described in detail, it is tobe particularly understood that the invention is not limited thereto orthereby.

l claim:

1. A luminescent material having the general formulation3Cd3(PO4)z-xNaFyMn:zPb, where x is not less than 2.5 moles and not morethan 5.5 moles, y is not less' than 0.1% by weight and not more than 1%by weight of cadmium ortliophosphate, z is not less than 5"% and notmore than 7% by weight of cadmium orthophosphate, and there ischemically combined with said luminescent material from l to 50 molarpercent of excess P205 over the total moles of cadmium orthophosphate.

2. The method of preparing a leadand manganeseactivated cadmium-sodiumuorphosphate luminescent material having as essential elements Cd, F, P,0, Na, Mn and Pb, comprising mixing the following raw mix components:cadmiumand phosphorusand oxygencontaining material which on tiring willform Cds(P04)2 with an excess of P205 and which material is free fromnon-volatile constituents other than said essential elements; sodiumandilumine-containing material which will form NaF and which material isfree from nonvolatile constituents other than` said essential elements;manganese-containing material which will form one of the groupconsisting of MnO and Mua(P04)z and which manganese-containing materialis free from non-volatile consitutents other than said essentialelements; and leadcontaining material which will form one of the groupconsisting of PbO and Pb3(P04)2 and which lead-containing material isfree from non-volatile constituents other than said essential elements,said essential elementcontaining materials being present in thefollowing stated proportions: said Cda(PO4)2 and excessl P205 formingmaterial being present in amounts sufficient -to form 3 moles ofCda(P04)2 and anv excess of from 1 to 50 molar percent of P205; said NaFforming material being present in amounts suicient to formv from 2.5- to5.5 moles NaF; said manganese-containing material being. present inamounts sufficient to produce from 0.029 mole to 0.29 mole MnO; saidlead-containing material being present in amounts suicient to producelfrom 0;038 mole to` 0.54 mole Pb0`; the total excess of said P205 notexceeding 50 molar percent of the cadmium orthophosphateg-milling theforegoing raw-mix components, and firing said milled raw-mix componentsat from 450 C. to 600 C. for at least one hour.

SThe method of lpreparing a leudand manganeseactivated cadmium-sodiumfluorophosphate' luminescent material having as essential elements Cd,F, P, 0, Na, Mn and Pb, comprising mixing the following raw mixcomponents: cadmiurn-r and phosphorusand oxygencontaining material whichon firing will form Cd3(P04)2 with excessof P205 and whichy material isfree from non-Volatile constituents other than said essential elements;sodi'urnand fluorine-containing material which will form Nali2 and whichmaterial is free from nonvolatile constituents other than said essentialelements, manganese-containing material which will form one of the groupconsisting of MnO and Mn3(P04)2 and which manganese-containing materialis free from non-volatile constituents other than said essentialelements; and leadcontaining. material which will form one of the groupconsisting of PbO and Pb3(P04)'2 and which lead-containing material isfree from non-volatile constituents other than said essential elements,said essential elementcontaining materials being present in thefollowing stated proportions: said Cda(P04)2 and excess P205 formingmaterial being present in amounts suliicient to form 3 moles ofCda(P0i)2 and an excess of. about 25 molar percent of P205; said Nal?forming material being present in amounts sucient to form about 4 molesNaF; said manganese-containing material being present in amountssufcient to produce about 0.115 mole M; said leadcontaining materialbeing present in amounts sufficient to produce about 0.306 mole PbO;miliing the foregoing raw-mix components, and tiring said milled raw-mixcomponents at from 450 C. to 600 C. for at least one hour.

4. The method of preparing a luminescent material comprising mixing thefollowing raw-mix components in the stated proportions: cadmium oxide, 9moles; diammonium acid phosphate, 7.5 moles; manganous carbonate, 0.115mole; sodium fluoride, 4 moles; and plumbous nitrate, 0.305 mole;milling the foregoing raw-mix components;` and firing said milledraw-mix components at from 450 C. to 600 C. for at least one hour.

References Cited in the tile of this patent Chem. Abstracts, vol. 49,No. l, January 10, 1955, page 63.

1. A LIMINESCENT MATERIAL HAVING THE GENERAL FORMULATION3CD3(PO4)2''XNAFYMN:ZPB, WHERE X IS NOT LESS THAN 2.5 MOLES AND NOT MORETHAN 5.5 MOLES, Y IS NOT LESS THAN 0.1% BY WEIGHT AND NOT MORE THAN 1%BY WEIGHT OF CADMIUM ORTHOPHOSPHATE, Z IS NOT LESS THAN 0.5 AND NOT MORETHAN 7% BY WEIGHT OF CADMIUM ORTHOPHOSPHATE, AND THERE IS CHEMICALLYCOMBINED WITH SAID LUMINESCENT MATERIAL FROM 1 TO 50 MOLAR PERCENT OFEXCESS P2O5 OVER THE TOTAL MOLES OF CALMIUN ORTHOPHOSPHATE.